The present invention relates to a filled tubular article for controlled insertion into a molten metal as it is being cast for altering same.
The addition of alloying and treating agents into a molten metal such as iron by insertion of an elongated rod-like article into a casting mold's downsprue is becoming more well known in the art. More sophisticated equipment has recently been developed to controllably insert such filled tubular articles into the casting mold during metal pouring at precisely the rate and point required to obtain the desired castings with minimum waste.
For the most part, the filled tubular articles are manufactured by depositing powdered ingredients or particulate material onto a strip of metal that may be partly formed into a trough. Thereafter, the strip of metal, which is usually steel because of its formability, is formed into a tube by conventional methods and the tube passed axially through a forming die in order to reduce its external diameter and to compact the powdered ingredients within it. Unfortunately, the thickness of the tubes is greater than that desired for fast dissolution in the molten metal. For example, if attempts are made to make the radial thickness of the tubes below about 0.25 mm (0.010") then the edges of the strip fail to remain in abutment and can allow some of the particulate material to fall out. On the other hand, if the strip edges are overlapped to form the tube, then when the article is inserted into the molten metal the melting rate around its periphery is unequal.
Because of the relatively poor dissolution or melting rate of the relatively thick prior art metal tubes, it has been found necessary to limit the speed at which they are fed to the molten metal in order to prevent the unmelted remaining portions of the tubes from penetrating the sides of the casting mold's downsprue. In some instances this has required that two or more filled tubular articles be simultaneously inserted into the molten metal at additional expense in order to obtain the desired quantity of treating agent or inoculant at the required rate.
We recently recognized that the dissolution rate of a steel tube could be controllably increased by careful selection of the chemical composition of the particulate treating agents within the tube, for example the percentage range of silicon in a ferrosilicon based inoculant, and by controlling the degree of compaction of such agents while maintaining the temperature of the molten metal at a preselected low value. Although the tube would melt faster if exposed to molten metal at a higher temperature, it is desirable to maintain such temperature at a low value in order to avoid waste of energy and to avoid the need for additional inoculants because of the fading characteristics of many treating agents. Tests have indicated that the steel tube can be melted internally to a significant degree by solid state diffusion. Simultaneously, the steel tube dissolves externally as a result of erosion and diffusion upon being exposed to the ingredients of the molten metal, even though the melting temperature of the tube is above the temperature of the molten metal.
Although we believe our solid state diffusion principle noted immediately above is a considerable advancement in the art by recognizing that as much as 30% or more of the thickness of the tube can be dissolved from within the tube, a still faster rate of internal dissolution is desirable in many cases in order to more quickly place the desired amount of treating agent into the molten metal without the tube making contact with the casting mold itself, and to simplify the feeding mechanism required.
In view of the above, it would be advantageous to so construct the filled tubular article that it would have a faster rate of internal dissolution when inserted into a molten metal.